Dual-clutch transmission with multiple first gears

ABSTRACT

A dual-clutch transmission assembly is disclosed that splits the torque generated by an engine between first and second layshafts. A first input hub is connected to the first layshaft by a first clutch and a second input hub is connected to the second layshaft by a second clutch. A first gearset is carried on the first layshaft and a second gearset is carried on the second layshaft. The first gearset includes a primary first gear and the second gearset includes a duplicate first gear. The first and second layshafts receive torque from the transmission input shaft in response to contemporaneous engagement of the primary first gear, the duplicate first gear, and the first and second clutches, which can be used during vehicle launch to split the torque applied to the first and second clutches.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/082,696, filed on Nov. 21, 2014 and 62/121,756, filed on Feb. 27,2015. This application is related to U.S. application Ser. No.14/941,484, filed on Nov. 13, 2015. The entire disclosures of theapplications referenced above are incorporated herein by reference.

FIELD

The present disclosure generally relates to the field of dual-clutchtransmissions (DCT). More specifically, a dual-clutch transmissionassembly is disclosed with multiple first gears that split the torquegenerated by an engine of a vehicle into multiple torque flow paths.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Conventional dual-clutch transmissions (DCT) combine two manualtransmissions into a single transmission assembly. Accordingly,dual-clutch transmissions provide a design alternative to conventionalmanual and automatic transmissions and can offer increased efficiencywhen properly configured for a particular vehicle. With increasing fuelcosts, vehicle fuel economy has become an important design considerationin recent years contributing to a rise in the number of dual-clutchtransmissions being installed in vehicles, particularly in theautomotive market.

Dual-clutch transmissions typically include two layshafts, eachsupporting a plurality of gears. Each layshaft also has a clutchinterconnecting the layshaft to a hub and each clutch connects anddisconnects each respective layshaft from the engine. One of thelayshafts may include only odd numbered gears while the other layshaftmay include only even numbered gears so that clutch-to-clutch power-onshifts can be accomplished in a similar manner to the shifting of aplanetary automatic transmission. Accordingly, one of the layshafts maycarry a first gear while the other layshaft carries a second gear and soon. The number of forward gear ratios provided thus equals a sum of thenumber of gears disposed along the two layshafts. Additional gear ratiosthus require the addition of odd and even numbered gears to thelayshafts, which contributes to a larger, heavier, costlier, and lessefficient dual-clutch transmission.

During vehicle launch, conventional dual-clutch transmissions engage thefirst gear and the clutch that is connected to the layshaft supportingthe odd numbered gears. Accordingly, all of the torque from the engineis directed through this one clutch. To reduce the noise, vibration, andharshness of the vehicle launch, some slip of this clutch is permitteduntil a minimum required vehicle speed is achieved and clutch lock-uptorque disturbance is within pre-designated limits. This clutch slip,particularly for extended durations of time, requires an effectivecooling strategy for the clutch. Where the clutch is a wet clutch,cooling is achieved by high volume fluid flow through the clutch, whichmay reach up to 20 liters per minute. Such coolant flow requirementslead to an increase in pump size and/or number, which increasesparasitic losses and thereby decreases the efficiency of the dual-clutchtransmission. Accordingly, dry clutches are typically more efficientsince pump related losses can be reduced or eliminated. However, suchdry clutches rely on less efficient air-cooling and repeated launchescan lead to overheating of the clutch. Limiting slip time or alternatingfirst gear launches with second gear launches (thus utilizing the clutchfor the even numbered gears while the clutch for the odd numbered gearscools) has been used as a strategy to avoid structural damage to theclutch and/or transmission, but there are several drawbacks associatedwith these strategies. Mainly, torque jerks, slower acceleration, andincreased noise, vibration, and harshness occur.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In accordance with one aspect of the subject disclosure, a dual-clutchtransmission assembly is provided that splits the torque generated bythe engine of a vehicle between first and second layshafts. The torquesplit dual-clutch transmission assembly generally includes atransmission input shaft that receives torque from the engine of thevehicle and a transmission output shaft that supplies torque todrivetrain components of the vehicle. First and second input hubsdisposed adjacent to the first and second layshafts are rotatablycoupled with the transmission input shaft.

A first clutch is disposed between and interconnects the first input huband the first layshaft. Accordingly, the first clutch selectivelycouples rotation of the first input hub with the first layshaft. Asecond clutch is disposed between and interconnects the second input hubwith the second layshaft. Thus, the second clutch selectively couplesrotation of the second input hub with the second layshaft. A firstgearset that is rotatably coupled to and carried on the first layshafttransfers torque between the first layshaft and the transmission outputshaft. A second gearset that is rotatably coupled to and carried on thesecond layshaft transfers torque between the second layshaft and thetransmission output shaft. The first gear set includes a primary firstgear having a primary first gear diameter and the second gearsetincludes a duplicate first gear that has a duplicate first gear diameterthat is equal to the primary first gear diameter. The first and secondlayshafts both receive torque from the transmission input shaft inresponse to contemporaneous engagement of the primary first gear, theduplicate first gear, the first clutch, and the second clutch. As aresult, the torque produced by the engine is split between the first andsecond clutches and is directed through both the primary first gear andthe duplicate first gear at the same time. Advantageously, the first andsecond clutches can be engaged contemporaneously during launch of thevehicle to split the torque produced by the engine between the first andsecond clutches, which in turn reduces heat generation in the firstclutch and in the second clutch.

In accordance with another aspect of the subject disclosure, thedual-clutch transmission assembly includes at least one transmissioninput shaft, a first input member that is rotatably coupled to the atleast one transmission input shaft, and a second input member that isdisposed co-axially within the first input member. The dual-clutchtransmission assembly also includes a first shaft that is hollow andthat is aligned with the first input member and a second shaft that isdisposed co-axially within the first shaft. The first clutch is disposedbetween the first input member and the first shaft. Accordingly, thefirst clutch selectively couples the first input member and the firstshaft such that the first shaft rotates with the first input member. Thesecond clutch is disposed between the second input member and the secondshaft. Accordingly, the second clutch selectively couples the secondinput member and the second shaft such that the second shaft rotateswith the second input member.

The dual-clutch transmission assembly may further include a third shaftand a planetary gearset that is disposed between and interconnects thefirst and third shafts. The third shaft is hollow and extends co-axiallyabout the second shaft at a location that is axially spaced from thefirst shaft. The first gearset is rotatably coupled to and carried onthe third shaft and the second gearset is rotatably coupled to andcarried on the second shaft. The dual-clutch transmission assembly mayalso include an output member and an output gearset. The output memberextends co-axially about the first and second gearsets and is rotatablycoupled to the transmission output shaft. The output gearset isrotatably coupled to and carried on the output member and is arranged inmeshing engagement with the first and second gearsets. In operation,each of the second and third shafts receives torque in response tocontemporaneous engagement of the primary first gear, the duplicatefirst gear, the first clutch, and the second clutch. Advantageously, thefirst and second clutches can be engaged contemporaneously during launchof the vehicle to split the torque applied to the first and secondclutches and to reduce heat generation in the first clutch and in thesecond clutch.

Since the torque split dual-clutch transmission assemblies disclosedherein reduce heat generation in the first and second clutches, a moreefficient, more durable, and better performing transmission is realized.Where the first and second clutches are wet clutches, the coolant flowrequirements of the clutches are reduced leading to reduced pumpinglosses and increased efficiency. Where the first and second clutches aredry clutches, less heat generation results in fewer clutch failures, thepossibility of longer slip times, and first gear launches can beutilized exclusively (as opposed to alternating between first and secondgear launches) for improved acceleration and reduced noise, vibration,and harshness. In addition, the clutch size and clutch coolingprovisions can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a schematic view of an exemplary dual-clutch transmissionassembly constructed in accordance with the subject disclosure wherethird and fourth gearsets are arranged on first and second intermediateshafts respectively;

FIG. 2 is a schematic view of another exemplary dual-clutch transmissionassembly constructed in accordance with the subject disclosure where thethird and fourth gearsets are arranged one after the other on a singleintermediate shaft;

FIG. 3 is a schematic view of another exemplary dual-clutch transmissionassembly constructed in accordance with the subject disclosure wheregears of the third and fourth gearsets are sequentially arranged alongthe single intermediate shaft;

FIG. 4 is a schematic view of another exemplary dual-clutch transmissionassembly constructed in accordance with the subject disclosure where aprimary first gear and a duplicate first gear are meshingly engaged witha first output gear that is carried on the single intermediate shaft;

FIG. 5 is a schematic view of another exemplary dual-clutch transmissionassembly constructed in accordance with the subject disclosure where theprimary first gear and the duplicate first gear are meshingly engagedwith the first output gear and where a second gear and a reverse gearare meshingly engaged with a second output gear that is carried on thesingle intermediate shaft;

FIG. 6 is a schematic view of another exemplary dual-clutch transmissionassembly constructed in accordance with the subject disclosure where atransfer clutch extends between third and fourth output gears toselectively provide additional gear ratios without increasing the numberof output gears;

FIG. 7 is a schematic view of another exemplary dual-clutch transmissionassembly constructed in accordance with the subject disclosure where asecond gear and a second transfer gear are meshingly engaged with asecond output gear and a third gear and a third transfer gear aremeshingly engaged with the third output gear to provide additional gearratios without increasing the number of output gears;

FIG. 8 is a schematic view of another exemplary dual-clutch transmissionassembly constructed in accordance with the subject disclosure where thedual-clutch transmission assembly has a planetary configuration with twosets of pinion gears;

FIG. 9 is a schematic view of another exemplary dual-clutch transmissionassembly constructed in accordance with the subject disclosure where thedual-clutch transmission assembly has a planetary configuration with oneset of pinion gears; and

FIG. 10 is a schematic view of another exemplary dual-clutchtransmission assembly constructed in accordance with the subjectdisclosure where the dual-clutch transmission assembly has a planetaryconfiguration with a primary first gear and a duplicate first gear thatare meshingly engaged with a common output gear.

DETAILED DESCRIPTION

Referring to the Figures, wherein like numerals indicate correspondingparts throughout the several views, a dual-clutch transmission assembly20 is disclosed. It should be appreciated that in operation, thedual-clutch transmission assembly 20 splits the torque generated by anengine 22 of a vehicle and applies the torque to the wheels 24 of avehicle through one or more drivetrain components 26.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

Referring to FIG. 1, the dual-clutch transmission assembly 20 includes atransmission input shaft 28 that receives torque from the engine 22 ofthe vehicle. The dual-clutch transmission assembly 20 also includes atransmission output shaft 30 that supplies torque to the wheels 24 ofthe vehicle through drivetrain components 26 such as the final driveassembly 26. Accordingly, the dual-clutch transmission assembly 20receives torque through the transmission input shaft 28, which maygenerally be positioned at one end 32 of the dual-clutch transmissionassembly 20 and outputs torque through the transmission output shaft 30,which may generally be positioned at an opposite end 34 of thedual-clutch transmission assembly 20. The dual-clutch transmissionassembly 20 may thus be installed in a vehicle between the engine 22 ofthe vehicle and the various drivetrain components 26, which may includewithout limitation, a final drive assembly. It should be appreciatedthat such drivetrain components 26 ultimately couple the transmissionoutput shaft 30 to one or more wheels 24 of the vehicle such that thewheels 24 of the vehicle are rotatably driven by rotation of thetransmission output shaft 30.

As shown in FIG. 1, a transmission input gear 36 is rotatably coupledand carried on the transmission input shaft 28 and a transmission outputgear 38 is rotatably coupled to and carried on the transmission outputshaft 30. By way of example and without limitation, the transmissioninput gear 36 may be fixed to the transmission input shaft 28 by asplined, bolted, or welded connection or may be integral with thetransmission input shaft 28 and the transmission output gear 38 may befixed to the transmission output shaft 30 by a splined, bolted, or awelded connection or may be integral with the transmission output shaft30. The transmission input gear 36 has a transmission input geardiameter 40 and the transmission output gear 38 has a transmissionoutput gear diameter 42. The transmission input shaft 28 and thetransmission output shaft 30 may generally be aligned with one anotherand spaced from one another by a longitudinally extending gap 44. Thedual-clutch transmission assembly further includes a first layshaft 46and a second layshaft 48. In FIG. 1, the first layshaft 46 extendsparallel to and is transversely spaced from the transmission input shaft28 and the second layshaft 48 extends parallel to and is transverselyspaced from the transmission input shaft 28 and the first layshaft 46.Thus, the first and second layshafts 46, 48 are parallel with oneanother. The first and second layshafts 46, 48 may generally be parallelto and transversely spaced from the longitudinally extending gap 44 andmay extend across the longitudinally extending gap 44. The first andsecond layshafts 46, 48 may also be arranged in a common plane 50 alongwith the transmission input and output shafts 28, 30 for a more compactarrangement of the dual-clutch transmission assembly 20. However, itshould be appreciated that other arrangements are possible and arewithin the scope of the subject disclosure.

The first layshaft 46 is generally aligned with a first input hub 52that is disposed adjacent the transmission input shaft 28. Similarly,the second layshaft 48 is aligned with a second input hub 56 that isalso disposed adjacent the transmission input shaft 28. A first clutch60 is disposed between and interconnects the first input hub 52 and thefirst layshaft 46. A second clutch 62 is disposed between andinterconnects the second input hub 56 and the second layshaft 48. Whenthe first and second clutches 60, 62 are engaged during operation of thedual-clutch transmission assembly 20, the first clutch 60 selectivelycouples rotation of the first input hub 52 with rotation of the firstlayshaft 46 and the second clutch 62 selectively couples rotation of thesecond input hub 56 with rotation of the second layshaft 48. It shouldfurther be appreciated that the first and second clutches 60, 62 may be,without limitation, wet clutches or dry clutches and may be constructedof various known components including, without limitation, clutchplates, actuators, and friction surfaces.

A first layshaft input gear 64 is rotatably coupled to and carried onthe first input hub 52 and is arranged in meshing engagement with thetransmission input gear 36. Accordingly, the first layshaft input gear64 transfers rotational energy and torque from the transmission inputgear 36 to the first input hub 52 during operation of the of thedual-clutch transmission assembly 20. Similarly, a second layshaft inputgear 66 is rotatably coupled to and carried on the second input hub 56and is arranged in meshing engagement with the transmission input gear36 opposite the first layshaft input gear 64. Accordingly, the secondlayshaft input gear 66 transfers rotational energy and torque from thetransmission input gear 36 to the second input hub 56 during operationof the dual-clutch transmission assembly 20. By way of non-limitingexample, the first layshaft input gear 64 may be fixed to the firstinput hub 52 by a splined, bolted, or welded connection or may beintegral with the first input hub 52 and the second layshaft input gear66 may be fixed to the second input hub 56 by a splined, bolted, orwelded connection or may be integral with the second input hub 56.

A first gearset 68 is rotatably coupled to and carried on the firstlayshaft 46. As shown in FIG. 1, the first gearset 68 includes a primaryfirst gear 70, a plurality of odd numbered gears 72, and a reverse gear74. Although any number of odd numbered gears 72 and reverse gears 74may be utilized without departing from the scope of the presentdisclosure, including a single odd numbered gear, the plurality of oddnumbered gears 72 illustrated in FIG. 1 includes a third gear 76 and afifth gear 78. A second gearset 80 is rotatably coupled to and carriedon the second layshaft 48. The second gearset 80 includes a duplicatefirst gear 82 and a plurality of even numbered gears 84. Again, whileany number of even numbered gears 84 may be utilized, including a singleeven numbered gear, the plurality of even numbered gears 84 illustratedin FIG. 1 includes a second gear 86, a fourth gear 88, and a sixth gear90. Of course it should be appreciated that this arrangement of gears ismerely exemplary and that other arrangements are envisioned. By way ofexample and without limitation, placement of the reverse gear 74 may bereversed where the reverse gear 74 is rotatably coupled to and carriedon the second layshaft 48. Further it should be appreciated that theterm “rotatably coupled to” as used herein means that the gears of thefirst gearset 68 and the gears of the second gearset 80, when engaged,rotate with the first layshaft 46 and the second layshaft 48respectively. Engagement of the gears of the first gearset 68 with thefirst layshaft 46 and engagement of the gears of the second gearset 80with the second layshaft 48 can be accomplished by any of the couplingsknown in the art, including without limitation, dog clutches ormechanical diodes (not shown). Alternatively, the gears of the firstgearset 68 and the gears of the second gearset 80 may always be engagedwhere the gears of the first gearset 68 and the gears of the secondgearset 80 are fixed to the first and second layshafts 46, 48respectively. By way of example and without limitation, the gears of thefirst and second gearsets 68, 80 may be fixed to the first and secondlayshafts 46, 48 respectively by a splined, bolted, or welded connectionor may be integral with the first and second layshafts 46, 48. The term“carried on” as used herein means that the gears of the first gearset 68and the gears of the second gearset 80 are disposed on and are supportedby the first layshaft 46 and the second layshaft 48 respectively.

Still referring to FIG. 1, the dual-clutch transmission assembly 20includes a first intermediate shaft 92 and a second intermediate shaft94. The first intermediate shaft 92 extends parallel to the firstlayshaft 46 and is transversely spaced from the first layshaft 46. Morespecifically, the first intermediate shaft 92 is positioned adjacent thefirst layshaft 46 and may be positioned between the first layshaft 46and the second layshaft 48. The second intermediate shaft 94 extendsparallel to the second layshaft 48 and is transversely spaced from thesecond layshaft 48. More specifically, the second intermediate shaft 94is positioned adjacent the second layshaft 48 and may also be positionedbetween the first layshaft 46 and the second layshaft 48. Therefore, thefirst and second layshafts 46, 48 may be arranged parallel to oneanother and the first and second intermediate shafts 92, 94 may bearrangement parallel to one another and parallel to the first and secondlayshafts 46, 48. Further, the first and second intermediate shafts 92,94 may be positioned between the first and second layshafts 46, 48 suchthat the first and second intermediate shafts 92, 94 are positioned inthe same common plane 50 as the first and second layshafts 46, 48. Wherethe first and second intermediate shafts 92, 94 are positioned in thesame common plane 50 as the first and second layshafts 46, 48, thedual-clutch transmission assembly 20 may be constructed in a compactmanner such that packaging advantages may be realized.

A third gearset 96 is rotatably coupled to and carried on the firstintermediate shaft 92. The third gearset 96 is also arranged in meshingengagement with the primary first gear 70, the plurality of odd numberedgears 72, and the reverse gear 74 of the first gearset 68. Accordingly,the gears of the third gearset 96 are aligned with correspondingcounter-part gears of the first gearset 68 such that the first gearset68 transfers rotational energy and torque from the first layshaft 46 tothe third gearset 96 and thus the first intermediate shaft 92 duringoperation of the of the dual-clutch transmission assembly 20. By way ofexample and without limitation, the third gearset 96 may morespecifically include: a primary first output gear 98 arranged in meshingengagement with the primary first gear 70 of the first gearset 68, athird output gear 100 arranged in meshing engagement with the third gear76 of the first gearset 68, a fifth output gear 102 arranged in meshingengagement with the fifth gear 78 of the first gearset 68, and a reverseoutput gear 104 arranged in meshing engagement with the reverse gear 74of the first gearset 68.

Similarly, a fourth gearset 106 is rotatably coupled to and carried onthe second intermediate shaft 94. The fourth gearset 106 is arranged inmeshing engagement with the duplicate first gear 82 and the plurality ofeven numbered gears 84 of the second gearset 80. Accordingly, the gearsof the fourth gearset 106 are aligned with corresponding counter-partgears of the second gearset 80 such that the second gearset 80 transfersrotational energy and torque from the second layshaft 48 to the fourthgearset 106 and thus the second intermediate shaft 94 during operationof the of the dual-clutch transmission assembly 20. By way of exampleand without limitation, the fourth gearset 106 may more specificallyinclude: a duplicate first output gear 108 arranged in meshingengagement with the duplicate first gear 82 of the second gearset 80, asecond output gear 110 arranged in meshing engagement with the secondgear 86 of the second gearset 80, a fourth output gear 112 arranged inmeshing engagement with the fourth gear 88 of the second gearset 80, anda sixth output gear 114 arranged in meshing engagement with the sixthgear 90 of the second gearset 80. Engagement of the gears of the thirdgearset 96 with the first intermediate shaft 92 and engagement of thegears of the fourth gearset 106 with the second intermediate shaft 94can be accomplished by any of the couplings known in the art, includingwithout limitation, dog clutches or mechanical diodes (not shown).Alternatively, the gears of the third gearset 96 and the gears of thefourth gearset 106 may always be engaged where the gears of the thirdgearset 96 and the gears of the fourth gearset 106 are fixed to thefirst and second intermediate shafts 92, 94 respectively. By way ofexample and without limitation, the gears of the third and fourthgearsets 96, 106 may be fixed to the first and second intermediateshafts 92, 94 respectively by a splined, bolted, or welded connection ormay be integral with the first and second intermediate shafts 92, 94.

A first intermediate shaft output gear 116 is rotatably coupled to andcarried on the first intermediate shaft 92. The first intermediate shaftoutput gear 116 is arranged in meshing engagement with the transmissionoutput gear 38 such that the first intermediate shaft output gear 116transfers rotational energy and torque from the first intermediate shaft92 to the transmission output gear 38 and thus the transmission outputshaft 30 during operation of the of the dual-clutch transmissionassembly 20. A second intermediate shaft output gear 118 is rotatablycoupled to and carried on the second intermediate shaft 94. The secondintermediate shaft output gear 118 is arranged in meshing engagementwith the transmission output gear 38 opposite the first intermediateshaft output gear 116. Accordingly, the second intermediate shaft outputgear 118 transfers rotational energy and torque from the secondintermediate shaft 94 to the transmission output gear 38 and thus thetransmission output shaft 30 during operation of the of the dual-clutchtransmission assembly 20. In this way, torque may be applied to thetransmission output gear 38 and thus the transmission output shaft 30simultaneously by both the first intermediate shaft 92 and the secondintermediate shaft 94 through the first intermediate shaft output gear116 and the second intermediate shaft output gear 118 respectively. Byway of non-limiting example, the first intermediate shaft output gear116 may be fixed to the first intermediate shaft 92 by a splined,bolted, or welded connection or may be integral with the firstintermediate shaft 92 and the second intermediate shaft output gear 118may be fixed to the second intermediate shaft 94 by a splined, bolted,or welded connection or may be integral with the second intermediateshaft 94.

Each of the first and second layshafts 46, 48 receives torque from thetransmission input shaft 28 in response to contemporaneous engagement ofthe primary first gear 70, the duplicate first gear 82, the first clutch60, and the second clutch 62. Such contemporaneous engagement may beeffectuated during launch of the vehicle to split the torque applied tothe first and second clutches 60, 62. It should be appreciated that theterm “contemporaneous”, as used herein, means that the primary firstgear 70, the duplicate first gear 82, and the first and second clutches60, 62 are all in an engaged state at a single moment in time; however,this term does not require the primary first gear 70, the duplicatefirst gear 82, and the first and second clutches 60, 62 to be switchedto the engaged state or switched back to a disengaged state at the sametime as sequential engagement of the primary first gear 70, theduplicate first gear 82, and the first and second clutches 60, 62 isalso envisioned and within the scope of the subject disclosure.Advantageously, this arrangement reduces the amount of heat generated inthe first clutch 60 and/or in the second clutch 62 during operation ofthe dual-clutch transmission assembly 20, especially during repeatedvehicle launches where heat generation in the first clutch 60 and/orsecond clutch 62 can be problematic and detrimental to the structuralintegrity and performance of the first clutch 60 and/or second clutch62.

During vehicle launch, the primary first gear 70, the duplicate firstgear 82, and the first and second clutches 60, 62 are engaged such thatthe torque applied to the transmission input shaft 28 is split into twotorque flow paths 120, 122 including a first torque flow path 120 and asecond torque flow path 122 that pass through the first and secondlayshafts 46, 48, respectively. The two torque flow paths 120, 122 passfrom the first and second layshafts 46, 48, through the primary firstgear 70 and the duplicated first gear 82, through the primary firstoutput gear 98 and the duplicate first output gear 108, and thus to thefirst and second intermediate shafts 92, 94. The two torque flow paths120, 122 are then re-combined at the transmission output gear 38. Inthis way, each of the first and second clutches 60, 62 experience only aportion of the torque that is applied to the transmission input shaft28, therefore reducing heat generation in the first clutch 60 and/or thesecond clutch 62.

To provide different forward gear ratios, the gears of the first gearset68 and the gears of the second gearset 80 may be provided with differentdiameters. For example, the plurality of odd numbered gears 72 of thefirst gearset 68 may have gear diameters that increase with each highernumbered gear and the plurality of even numbered gears 84 of the secondgearset 80 may have gear diameters that increase with each highernumbered gear. As shown in FIG. 1, the primary first gear 70 may have aprimary first gear diameter 124, the third gear 76 may have a third geardiameter 126 that is larger than the primary first gear diameter 124,and the fifth gear 78 may have a fifth gear diameter 128 that is largerthan the third gear diameter 126. The second gear 86 may have a secondgear diameter 130, the fourth gear 88 may have a fourth gear diameter132 that is larger than the second gear diameter 130, and the sixth gear90 may have a sixth gear diameter 134 that is larger than the fourthgear diameter 132. The reverse gear 77 has a reverse gear diameter 136and the duplicate first gear 82 has a duplicate first gear diameter 138.The primary first gear diameter 124 is equal to the duplicate first geardiameter 138 such that the primary first gear 70 and the duplicate firstgear 82 may be engaged at the same time without causing the first andsecond intermediate shaft output gears 116, 118 to rotate at differentspeeds and in turn bind with the transmission output gear 38. Inaddition, since the primary first gear diameter 124 is equal to theduplicate first gear diameter 138, the primary first gear 70 and theduplicate first gear 82 distribute the torque produced by the engine 22evenly between the first clutch 60 and the second clutch 62 duringvehicle launch.

The gears of the third and fourth gearsets 96, 106 are also providedwith different diameters so that the gears of the third gearset 96 canmesh with the gears of the first gearset 68 and so that the gears of thefourth gearset 106 can mesh with the gears of the second gearset 80. Inkeeping with the arrangement described above and shown in FIG. 1, thegears of the third gearset 96 may decrease in diameter with each highernumbered gear. For example, the primary first output gear 98 may have aprimary first output gear diameter 140 that is larger than the primaryfirst gear diameter 124, the third output gear 100 may have a thirdoutput gear diameter 142 that is larger than the third gear diameter 126and smaller than the primary first output gear diameter 140, and thefifth output gear 102 may have a fifth output gear diameter 144 that issmaller than the fifth gear diameter 128 and the third output geardiameter 142. Similarly, the gears of the fourth gearset 106 maydecrease in diameter with each higher numbered gear. For example, thesecond output gear 110 may have a second output gear diameter 146 thatis larger than the second gear diameter 130, the fourth output gear 112may have a fourth output gear diameter 148 that is larger than thefourth gear diameter 132 and smaller than the second output geardiameter 146, and the sixth output gear 114 may have a sixth output geardiameter 150 that is smaller than the sixth gear diameter 134 and thefourth output gear diameter 148. The reverse output gear 104 may have areverse output gear diameter 152 that is larger than the reverse geardiameter 136 and the duplicate first output gear 108 may have aduplicate first output gear diameter 154 that is larger than theduplicate first gear diameter 138. As a result, a total of six differentforward gear ratios and a single reverse gear ratio are provided by thearrangement shown in FIG. 1.

In FIGS. 2 and 3, alternative configurations of the dual-clutchtransmission assembly 20 are illustrated where the first and secondintermediate shafts 92, 94 of the configuration shown in FIG. 1 havebeen replaced by a single intermediate shaft 156. Accordingly, thetransmission output gear 38, the first intermediate shaft output gear116, and the second intermediate shaft output gear 118 of theconfiguration shown in FIG. 1 may also be eliminated. Instead, thesingle intermediate shaft 156 may be directly coupled to thetransmission output shaft 30 or may be integral with the transmissionoutput shaft 30. In accordance with the configuration shown in FIGS. 2and 3, both the third and fourth gearsets 96, 106 are rotatably coupledto and carried on the single intermediate shaft 156. By way ofnon-limiting example, the gears of the third and fourth gearsets 96, 106may be selectively engaged to the single intermediate shaft 156 by dogclutches, mechanical diodes, and the like or may be fixed with thesingle intermediate shaft 156 by splined, bolted, or welded connectionsand the like. In FIG. 2, the third gearset 96 is disposed on the singleintermediate shaft 156 adjacent the fourth gearset 106 such that theprimary first output gear 98, the third output gear 100, the fifthoutput gear 102, and the reverse output gear 104 are disposed on oneside of the single intermediate shaft 156 while the second output gear110, the fourth output gear 112, the sixth output gear 114, and theduplicate first output gear 108 are disposed on an opposite side of thesingle intermediate shaft 156. Alternatively, in FIG. 3, the gears ofthe third and fourth gearsets 96, 106 are disposed along in the singleintermediate shaft 156 in sequential order where the gears are arrangedin the following exemplary order along the single intermediate shaft156: the primary first output gear 98, the second output gear 110, thethird output gear 100, the fourth output gear 112, the fifth output gear102, the sixth output gear 114, the duplicate first output gear 108, andthe reverse output gear 104. In both FIGS. 2 and 3, the singleintermediate shaft 156 is disposed adjacent to the first and secondlayshafts 46, 48. More particularly, the single intermediate shaft 156may be positioned between the first and second layshafts 46, 48 and maybe arranged parallel to the first and second layshafts 46, 48 such thatthe gears of the first and second gearsets 68, 80 are aligned in meshingengagement with the gears of the third and fourth gearsets 96, 106.Accordingly, FIGS. 2 and 3 show simplified and dimensionally smallerconfigurations that can provide additional cost and packagingadvantages.

In FIGS. 4 and 5, alternative configurations of the dual-clutchtransmission assembly 20 are illustrated. The arrangement of the primaryfirst gear 70 and the duplicate first gear 82 in these configurationsyields a more compact dual-clutch transmission assembly 20.Advantageously, the positioning of the duplicate first gear 82 in theseconfigurations allows the duplicate first gear 82 to be added withoutincreasing the overall dimensions (i.e. length, height, and width) ofthe dual-clutch transmission assembly 20. As a result, transmissionhousings from other dual-clutch transmission assemblies that do not havea duplicate first gear can be utilized with little to no modification.

In FIG. 4, the positioning of the duplicate first gear 82 along thesecond layshaft 48 has been modified from the position shown in FIGS. 2and 3. With reference to FIG. 4, the duplicate first gear 82 ispositioned in meshing engagement with a first output gear 99. Theprimary first gear 70 is also positioned in meshing engagement with thefirst output gear 99 such that the primary first gear 70, the duplicatefirst gear 82, and the first output gear 99 are all in alignment withone another. Stated another way, in FIG. 4, the primary first gear 70 isaxially positioned on the first layshaft 46 between the first clutch 60and the third gear 76 and the duplicate first gear 82 is axiallypositioned on the second layshaft 48 between the second clutch 62 andthe second gear 86. The primary first gear 70 and the duplicate firstgear 82 commonly share the first output gear 99 and both the primaryfirst gear 70 and the duplicate first gear 82 cooperate to drive thefirst output gear 99 when the first and second clutches 60, 62 areengaged.

The primary first gear diameter 124 and the duplicate first geardiameter 138 are equal such that the primary first gear 70 and theduplicate first gear 82 can be concurrently engaged with the firstoutput gear 99 without binding. The first output gear 99 is carried onand rotates with the single intermediate shaft 156. By way ofnon-limiting example, the first output gear 99 may be selectivelyengaged to the single intermediate shaft 156 by dog clutches, mechanicaldiodes, and the like or may be fixed with the single intermediate shaft156 by splined, bolted, or welded connections and the like. The firstoutput gear 99 has a first output gear diameter 141, which may be largerthan the second output gear diameter 146. During vehicle launch, theprimary first gear 70, the duplicate first gear 82, and the first andsecond clutches 60, 62 are engaged such that the torque applied to thetransmission input shaft 28 is split between the first torque flow path120 and the second torque flow path 122. The first torque flow path 120passes through the first clutch 60, through the primary first gear 70,through the first output gear 99, and to the single intermediate shaft156. Similarly, the second torque flow path 122 passes through thesecond clutch 62, through the duplicate first gear 82, through the firstoutput gear 99, and to the single intermediate shaft 156. Accordingly,the first and second torque flow paths 120, 122 are recombined at thefirst output gear 99. In this way, the duplicate first output gear 108shown in FIGS. 2 and 3 is eliminated for improved packaging, reducedcost, and weight savings.

The dual-clutch transmission 20 in FIG. 4 may optionally include areverse idler gear 75 disposed in meshing engagement between the reversegear 74 and the reverse output gear 104. The reverse idler gear 75reverses the rotation of the reverse output gear 104 relative to thereverse gear 74. Since the single intermediate shaft 156 rotates withthe reverse output gear 104 and the first layshaft 46 rotates with thereverse gear 74 when the reverse gear 74 is engaged, the reverse idlergear 75 allows the first layshaft 46 and the single intermediate shaft156 to rotate in opposite directions. Accordingly, the dual-clutchtransmission 20 illustrated in FIG. 4 may provide reverse by disengagingthe second clutch 62 and by engaging both the first clutch 60 and thereverse gear 74. In configurations where the reverse idler gear 75 isnot included, the first layshaft 46 may rotated in one direction whenone of the gears in the plurality of odd numbered gears 72 is engagedand the first layshaft 46 may rotate in an opposite direction when thereverse gear 74 is engaged. This reversal in the direction of rotationof the first layshaft 46 may be effectuated by reversing the directionof rotation of the transmission input shaft 28. The direction ofrotation of the transmission input shaft 28 may be reversed by separategearset (not shown) disposed between the engine 22 and the transmissioninput shaft 28. Alternatively, the direction of rotation of the engine22 itself may be reversed particularly where the engine 22 is electric.

In FIG. 5, the positioning of the duplicate first gear 82 along thesecond layshaft 48 and the positioning of the reverse gear 74 along thefirst layshaft 46 has been modified from the positions shown in FIGS. 2and 3. With reference to FIG. 5, both the primary first gear 70 and theduplicate first gear 82 are positioned in meshing engagement with thefirst output gear 99. Therefore, the primary first gear 70, theduplicate first gear 82, and the first output gear 99 of the dual-clutchtransmission 20 are all in alignment with one another. Like in FIG. 4,the first output gear 99 in FIG. 5 is carried on and rotates with thesingle intermediate shaft 156 and the first output gear diameter 141 ofthe first output gear 99 may be larger than the second output geardiameter 146. As in FIGS. 2 through 4, the second gear 86 in FIG. 5 ispositioned in meshing engagement with the second output gear 110.However, in the configuration shown in FIG. 5, the reverse gear 74 isalso positioned in meshing engagement with the second output gear 110via reverse idler gear 75. The reverse idler gear 75 is disposed inmeshing engagement between the reverse gear 74 and the second outputgear 110. Accordingly, the second gear 86, the second output gear 110,the reverse gear 74, and the idler gear 75 of the dual-clutchtransmission 20 are all in alignment with one another. Stated anotherway, in FIG. 5, both the primary first gear 70 and the reverse gear 74are axially positioned on the first layshaft 46 between the first clutch60 and the third gear 76 and the duplicate first gear 82 is axiallypositioned on the second layshaft 48 between the second clutch 62 andthe second gear 86. More specifically, the primary first gear 70 isaxially positioned on the first layshaft 46 between the first clutch 60and the reverse gear 74 and the reverser gear 74 is axially positionedon the first layshaft 46 between the third gear 76 and the primary firstgear 70. The reverse idler gear 75 reverses rotation of the secondoutput gear 110 relative to the reverse gear 74 such that the secondoutput gear 110 can be utilized when the second gear 86 is engaged andwhen the reverse gear 74 is engaged.

During vehicle launch, the primary first gear 70, the duplicate firstgear 82, and the first and second clutches 60, 62 illustrated in FIG. 5are engaged such that the torque applied to the transmission input shaft28 is split between the first torque flow path 120 and the second torqueflow path 122. The first torque flow path 120 passes through the firstclutch 60, through the primary first gear 70, through the first outputgear 99, and to the single intermediate shaft 156. Similarly, the secondtorque flow path 122 passes through the second clutch 62, through theduplicate first gear 82, through the first output gear 99, and to thesingle intermediate shaft 156. Accordingly, the first and second torqueflow paths 120, 122 are recombined at the first output gear 99. Aftervehicle launch, the dual-clutch transmission 20 may be shifted where theprimary first gear 70, the duplicate first gear 82, and the first clutch60 are disengaged. During the shift, the second gear 86 is engaged andthe second clutch 62 either remains engaged or is temporarily disengagedand then is re-engaged. Since the single intermediate shaft 156 rotateswith the second output gear 110 and the first layshaft 46 rotates withthe reverse gear 74 when the reverse gear 74 is engaged, the reverseidler gear 75 allows the first layshaft 46 and the single intermediateshaft 156 to rotate in opposite directions. Accordingly, the dual-clutchtransmission 20 illustrated in FIG. 5 may provide reverse by disengagingthe second clutch 62 and by engaging both the first clutch 60 and thereverse gear 74.

With reference to FIG. 5, the primary first gear 70 and the duplicatefirst gear 82 commonly share the first output gear 99 and both theprimary first gear 70 and the duplicate first gear 82 cooperate to drivethe first output gear 99 when both the first and second clutches 60, 62are engaged. In addition, the second gear 86 and the reverse gear 74commonly share the second output gear 110 where the second output gear110 is driven in one rotational direction by the second gear 86 when thefirst clutch 60 is disengaged and the second clutch 62 is engaged andwhere the second output gear 110 is driven in an opposite rotationaldirection by the reverse gear 74 and the reverse idler gear 75 when thefirst clutch 60 is engaged and the second clutch 62 is disengaged. Thisarrangement therefore eliminates both the duplicate first output gear108 and the reverse output gear 104 illustrated in FIGS. 2 and 3 forimproved packaging, reduced cost, and weight savings.

FIGS. 6 and 7 illustrate alternative configurations of the dual-clutchtransmission assembly 20 shown in FIG. 3. In FIGS. 6 and 7 thedual-clutch transmission assembly 20 of FIG. 3 has been modified toprovide additional ratios without increasing the number of gears andthus the dimensions of the dual-clutch transmission assembly 20. InFIGS. 6 and 7, the primary first output gear 98, the duplicate firstoutput gear 108, the second output gear 110, the third output gear 100,the fourth output gear 112, the fifth output gear 102, the sixth outputgear 114, and the reverse output gear 104 are carried on the singleintermediate shaft 156 and are selectively coupled with the singleintermediate shaft 156 such that they may be engaged and disengaged withthe single intermediate shaft 156. By way of example and withoutlimitation, engagement of the primary first output gear 98, theduplicate first output gear 108, the second output gear 110, the thirdoutput gear 100, the fourth output gear 112, the fifth output gear 102,the sixth output gear 114, and the reverse output gear 104 with thesingle intermediate shaft 156 may be accomplished by dog clutches,mechanical diodes, and the like. When any one of the primary firstoutput gear 98, the duplicate first output gear 108, the second outputgear 110, the third output gear 100, the fourth output gear 112, thefifth output gear 102, the sixth output gear 114, and the reverse outputgear 104 is engaged with the single intermediate shaft 156, that gearrotates with the single intermediate shaft 156. When any one of theprimary first output gear 98, the duplicate first output gear 108, thesecond output gear 110, the third output gear 100, the fourth outputgear 112, the fifth output gear 102, the sixth output gear 114, and thereverse output gear 104 is disengaged with the single intermediate shaft156, that gear rotates freely relative to the single intermediate shaft156 (i.e. free-wheels on the single intermediate shaft 156).

With reference to FIG. 6, the dual-clutch assembly 20 further includes atransfer clutch 157 that extends longitudinally between the third outputgear 100 and the fourth output gear 112. When the transfer clutch 157 isengaged, the transfer clutch 157 rotatably couples the third output gear100 with the fourth output gear 112 such that the third output gearrotates with the fourth output gear 112. When the transfer clutch 157 isdisengaged, the third output gear 100 may rotate at a different speedrelative to the fourth output gear 112. The transfer clutch 157 providestwo or more ratios where the third gear 76 acts as a driven gear. Thisstands in contrast to the configuration illustrated in FIG. 3, whereeach gear carried on the first and second layshafts 46, 48 (includingthe third gear 76) provides only a single ratio. Like in FIG. 3, oneratio for the third gear 76 is provided where the first clutch 60 isengaged (i.e. closed) and the second clutch 62 is disengaged (i.e.open). The third gear 76 is engaged and rotates with the first layshaft46, which drives rotation of the third output gear 100. The third outputgear 100 is engaged and rotates with the single intermediate shaft 156,which drives rotation of the output shaft 30. The transfer clutch 157 isdisengaged such that there is no torque transfer between the thirdoutput gear 100 and the fourth output gear 112 across the transferclutch 157. When this ratio for the third gear 76 is selected, powerflows from the transmission input shaft 28, through the transmissioninput gear 36, through the first layshaft input gear 64, through thefirst input hub 52, through the first clutch 60, through the firstlayshaft 46, through the third gear 76, through the third output gear100, through the single intermediate shaft 156, and to the output shaft156. An additional ratio for the third gear 76 is provided where thefirst clutch 60 is engaged (i.e. closed) and the second clutch 62 isdisengaged (i.e. open). The third gear 76 is engaged and rotates withthe first layshaft 46, which drives rotation of the third output gear100. Both the third output gear 100 and the fourth output gear 112 aredisengaged and rotate freely on the single intermediate shaft 156. Thetransfer clutch 157 is engaged such that the third output gear 100 andthe fourth output gear 112 rotate (i.e. free-wheel) together on thesingle intermediate shaft 156. The fourth output gear 112 is meshinglyengaged with the fourth gear 88 and drives the fourth gear 88. Thefourth gear 88 is engaged with the second layshaft 48. Any one of thegears carried on the second layshaft 48 may be engaged to send torqueback to the single intermediate shaft 156, thus creating the additionalratio. By way of example and without limitation, the sixth gear 90 maybe engaged with the second layshaft 48 such that the sixth gear 90 isdriven by the second layshaft 48, which is driven by the fourth gear 88.The sixth gear 90 is meshingly engaged with the sixth output gear 114and therefore drives rotation of the sixth output gear 114. The sixthoutput gear 114 is engaged with the single intermediate shaft 156, whichdrives rotation of the output shaft 30. Accordingly, to provide theadditional ratio for the third gear 76, power flows from thetransmission input shaft 28, through the transmission input gear 36,through the first layshaft input gear 64, through the first input hub52, through the first clutch 60, through the first layshaft 46, throughthe third gear 76, through the third output gear 100, through thetransfer clutch 157, through the fourth output gear 112, through thefourth gear 88, through the second layshaft 48, through the sixth gear90, through the sixth output gear 114, through the single intermediateshaft 156, and to the output shaft 30. Notwithstanding the exampleprovided above, it should be appreciated that any one of the other gearscarried on the second layshaft 48 may be engaged with the secondlayshaft 48 to be driven by the fourth gear 88 and re-direct torque backto the single intermediate shaft 156. Other alternatives are possiblewhere the second clutch 62 is engaged (i.e. closed) and the first clutch60 is disengaged (i.e. open) such that the fourth gear 88 acts as thedriven gear instead of the third gear 76.

In FIG. 7, the transfer clutch 157 of the dual-clutch assembly 20 shownin FIG. 6 is replaced by transfer gears 77, 87 that are disposed inmeshing engagement with the second output gear 110 and the third outputgear 100. Referring to FIG. 7, the transfer gears 77, 87 include a firsttransfer gear 77 and a second transfer gear 87. The first transfer gear77 is disposed in meshing engagement with the second output gear 110opposite the second gear 86. The first transfer gear 77 is carried onthe first layshaft 46 and is selectively coupled to the first layshaft46 such that the first transfer gear 77 rotates with the first layshaft46 when the first transfer gear 77 is engaged. The second transfer gear87 is disposed in meshing engagement with the third output gear 100opposite the third gear 76. The second transfer gear 87 is carried onthe second layshaft 48 and is selectively coupled to the second layshaft48 such that the second transfer gear 87 rotates with the secondlayshaft 48 when the second transfer gear 87 is engaged. By way ofexample and without limitation, the first and second transfer gears 77,87 may be selectively coupled to the first and second layshafts 46, 48respectively by dog clutches, mechanical diodes, and the like. The firsttransfer gear 77 has a first transfer gear diameter 131 that is equal tothe second gear diameter 130. The second transfer gear 87 has a secondtransfer gear diameter 127 that is larger than the first transfer geardiameter 131 and that is equal to the third gear diameter 126. Thetransfer gears 77, 87 provide two or more ratios where the second gear86 acts as the driven gear and two or more ratios where the third gear76 acts as the driven gear. This stands in contrast to the configurationillustrated in FIG. 3, where each gear carried on the first and secondlayshafts 46, 48 (including the second and third gears 76, 86) providesonly a single ratio. Like in FIG. 3, one ratio for the second gear 86 isprovided where the first clutch 60 is disengaged (i.e. open) and thesecond clutch 62 is engaged (i.e. closed). The second gear 86 is engagedand rotates with the second layshaft 48, which drives rotation of thesecond output gear 110. The second output gear 110 is engaged androtates with the single intermediate shaft 156, which drives rotation ofthe output shaft 30. The first transfer gear 77 is disengaged such thatthe first transfer gear 77 is free-wheeling on the first layshaft 46.When this ratio for the second gear 86 is provided, power flows from thetransmission input shaft 28, through the transmission input gear 36,through the second layshaft input gear 66, through the second input hub56, through the second clutch 62, through the second layshaft 48,through the second gear 86, through the second output gear 110, throughthe single intermediate shaft 156, and to the output shaft 30. Like inFIG. 3, one ratio for the third gear 76 is provided where the firstclutch 60 is engaged (i.e. closed) and the second clutch 62 isdisengaged (i.e. open). The third gear 76 is engaged and rotates withthe first layshaft 46, which drives rotation of the third output gear100. The third output gear 100 is engaged and rotates with the singleintermediate shaft 156, which drives rotation of the output shaft 30.The second transfer gear 87 is disengaged such that the second transfergear 87 is freewheeling on the second layshaft 48. When this ratio forthe third gear 76 is provided, power flows from the transmission inputshaft 28, through the transmission input gear 36, through the firstlayshaft input gear 64, through the first input hub 52, through thefirst clutch 60, through the first layshaft 46, through the third gear76, through the third output gear 100, through the single intermediateshaft 156, and to the output shaft 30.

An additional ratio for the second gear 86 is provided where the firstclutch 60 is disengaged (i.e. open) and the second clutch 62 is engaged(i.e. closed). The second gear 86 is engaged and rotates with the secondlayshaft 48, which drives rotation of the second output gear 110. Thesecond output gear 110 is disengaged and rotates freely on the singleintermediate shaft 156. The first transfer gear 77 is engaged with thefirst layshaft 46 such that the first transfer gear 77 rotates with anddrives the first layshaft 46. Any one of the other gears carried on thefirst layshaft 46 may be engaged to send torque back to the singleintermediate shaft 156, thus creating the additional ratio. By way ofexample and without limitation, the fifth gear 78 may be engaged withthe first layshaft 46 such that the fifth gear 78 is driven by the firstlayshaft 46, which is driven by the first transfer gear 77. The fifthgear 78 is meshingly engaged with the fifth output gear 102 andtherefore drives rotation of the fifth output gear 102. The fifth outputgear 102 is engaged with the single intermediate shaft 156, which drivesrotation of the output shaft 30. Accordingly, to provide the additionalratio for the second gear 86, power flows from the transmission inputshaft 28, through the transmission input gear 36, through the secondlayshaft input gear 66, through the second input hub 56, through thesecond clutch 62, through the second layshaft 48, through the secondgear 86, through the second output gear 110, through the first transfergear 77, through the first layshaft 46, through the fifth gear 78,through the fifth output gear 102, through the single intermediate shaft156, and to the output shaft 30. An additional ratio for the third gear76 is provided where the first clutch 60 is engaged (i.e. closed) andthe second clutch 62 is disengaged (i.e. open). The third gear 76 isengaged and rotates with the first layshaft 46, which drives rotation ofthe third output gear 100. The third output gear 100 is disengaged androtates freely on the single intermediate shaft 156. The second transfergear 87 is engaged such that the second transfer gear 87 rotates withthe second layshaft 48. Any one of the other gears carried on the secondlayshaft 48 may be engaged to send torque back to the singleintermediate shaft 156, thus creating the additional ratio. By way ofexample and without limitation, the sixth gear 90 may be engaged withthe second layshaft 48 such that the sixth gear 90 is driven by thesecond layshaft 48, which is driven by the second transfer gear 87. Thesixth gear 90 is meshingly engaged with the sixth output gear 114 andtherefore drives rotation of the sixth output gear 114. The sixth outputgear 114 is engaged with the single intermediate shaft 156, which drivesrotation of the output shaft 30. Accordingly, to provide the additionalratio for the third gear 76, power flows from the transmission inputshaft 28, through the transmission input gear 36, through the firstlayshaft input gear 64, through the first input hub 52, through thefirst clutch 60, through the first layshaft 46, through the third gear76, through the third output gear 100, through the second transfer gear87, through the second layshaft 48, through the sixth gear 90, throughthe sixth output gear 114, through the single intermediate shaft 156,and to the output shaft 156. Notwithstanding the examples providedabove, it should be appreciated that any one of the other gears carriedon the first layshaft 46 may be engaged with the first layshaft 46 to bedriven by the first transfer gear 77 and redirect torque back to thesingle intermediate shaft 156 and any one of the other gears carried onthe second layshaft 48 may be engaged with the second layshaft 48 to bedriven by the second transfer gear 87 and re-direct torque back to thesingle intermediate shaft 156. Further still, additional transfer gearsmay be provided to increase the number of possible gear combinations toprovide additional ratios.

FIGS. 8 and 9 illustrate a planetary configuration of the discloseddual-clutch transmission assembly 20. Referring to FIG. 8, thedual-clutch transmission assembly 20 includes at least one transmissioninput shaft 28 and a transmission output shaft 30 that are spaced fromone another by a longitudinal gap 44. Again, the at least onetransmission input shaft 28 may be rotatably coupled to an engine 22 andthe transmission output shaft 30 may be rotatably coupled to one or moredrivetrain components 26 that transfers torque to the wheels 24 of thevehicle. A first input member 158 is rotatably coupled to the at leastone transmission input shaft 28. Although the first input member 158 mayhave a variety of different shapes, the first input member 158 may havethe shape of a drum for example. A second input member 160 is disposedco-axially within the first input member 158. The second input member160 may also be rotatably coupled to the at least one transmission inputshaft 28. By way of non-limiting example, the first and second inputmembers 158, 160 may be fixed to the at least one transmission inputshaft 28 by a splined, bolted, or welded connection or may be integralwith the at least one transmission input shaft 28. The dual-clutchtransmission assembly 20 also includes a first shaft 162 that is alignedwith the first input member 158. The first shaft 162 is also hollow andreceives a second shaft 164 that is disposed co-axially within the firstshaft 162. A first clutch 60 is disposed between and interconnects thefirst input member 158 and the first shaft 162. When engaged, the firstclutch 60 couples rotation of the first input member 158 with the firstshaft 162. A second clutch 62 is disposed between and interconnects thesecond input member 160 and the second shaft 164. When engaged, thesecond clutch 62 couples rotation of the second input member 160 withthe second shaft 164.

The dual-clutch transmission assembly 20 further includes a third shaft166 that is hollow and that extends co-axially about the second shaft164 at a location that is axially spaced from the first shaft 162. Aplanetary gearset 168 is disposed between and interconnects the firstshaft 162 and the third shaft 166. The planetary gearset 168 includes asun gear 170, at least one pinion gear 172, 174, and a ring gear 176.The sun gear 170 is rotatably coupled to and is carried on the firstshaft 162 and the ring gear 176 is fixed to a ground 178. By way ofexample and without limitation, the sun gear 170 may be fixed to thefirst shaft 162 by a splined, bolted, or welded connection or may beintegral with the first shaft 162. By way of example and withoutlimitation, the ground 178 may be a housing of the dual-clutchtransmission assembly 20.

Still referring to FIG. 8, the at least one pinion gear 172, 174includes a first set of pinion gears 172 and a second set of piniongears 174. The first set of pinion gears 172 is disposed in meshingengagement with the sun gear 170. The second set of pinion gears 174 isdisposed in meshing engagement with the first set of pinion gears 172.The ring gear 176 is then disposed in meshing engagement with the secondset of pinion gears 174. A carrier 180 is disposed between and rotatablycouples the second set of pinion gears 174 and the third shaft 166.Therefore rotation of the carrier 180 drives the third shaft 166.

A first gearset 68 is rotatably coupled to and is carried on the thirdshaft 166 and a second gearset 80 is rotatably coupled to and is carriedon the second shaft 164. By way of non-limiting example, the gears ofthe first gearset 68 and the second gearset 80 may be selectivelyengaged to (by dog clutches, mechanical diodes, and the like) or fixedwith (by splined, bolted, or welded connections and the like) the secondand third shafts 164, 166. The axial arrangement of the first gearset 68and the second gearset 80 is such that the first gearset 68 is disposedaxially between the second gearset 80 and the planetary gearset 168. Thefirst gearset 68 includes a plurality of odd numbered gears 72 and areverse gear 74. In the exemplary configuration shown in FIG. 8, theplurality of odd numbered gears 72 of the first gearset 68 includes aprimary first gear 70, a third gear 77, and a fifth gear 78. The secondgearset 80 includes a plurality of even numbered gears 84 and aduplicate first gear 82. In the exemplary configuration shown, theplurality of even numbered gears 84 includes a second gear 86, a fourthgear 88, and a sixth gear 90.

An output member 182 extends co-axially about the first gearset 68 andthe second gearset 80. Although the output member 182 may have a varietyof different shapes, the output member 182 may have the shape of a drumfor example. The output member 182 is rotatably coupled to thetransmission output shaft 30 such that rotation of the output member 182drives the transmission output shaft 30. An output gearset 184 isrotatably coupled to and is carried on the output member 182. By way ofnon-limiting example, the gears of the output gearset 184 may beselectively engaged to the output member 182 by dog clutches, mechanicaldiodes, and the like or may be fixed to the output member 182 bysplined, bolted, or welded connections and the like. The output gearset184 is also arranged in meshing engagement with the first gearset 68 andthe second gearset 80. The output gearset 184 includes: a primary firstoutput gear 98 arranged in meshing engagement with the primary firstgear 70 of the first gearset 68, a second output gear 110 arranged inmeshing engagement with the second gear 86 of the second gearset 80, athird output gear 100 arranged in meshing engagement with the third gear76 of the first gearset 68, a fourth output gear 112 arranged in meshingengagement with the fourth gear 88 of the second gearset 80, a fifthoutput gear 102 arranged in meshing engagement with the fifth gear 78 ofthe first gearset 68, a sixth output gear 114 arranged in meshingengagement with the sixth gear 90 of the second gearset 80, a duplicatefirst output gear 108 arranged in meshing engagement with the duplicatefirst gear 82 of the second gearset 80, and a reverse output gear 104arranged in meshing engagement with the reverse gear 74 of the firstgearset 68. Accordingly, the first and second gearsets 68, 80 transferrotational energy and torque from the third shaft 166 and the secondshaft 164, respectively, to the output gearset 184 and thus the outputmember 182 during operation of the of the dual-clutch transmissionassembly 20 shown in FIG. 8.

As explained in connection with the configuration shown in FIG. 1, thegears of the first gearset 68 have diameters 124, 126, 128, 136 and thegears of the second gearset 80 have diameters 130, 132, 134, 138.Similarly, the gears of the output gearset 184 have diameters 140, 142,144, 146, 148, 150, 152, 154. The plurality of odd numbered gears 72 ofthe first gearset 68 shown in FIG. 8 may have gear diameters 124, 126,128 that increase with each higher numbered gear and the plurality ofeven numbered gears 84 of the second gearset 80 shown in FIG. 8 may havegear diameters 130, 132, 134 that increase with each high numbered gear.The gears of the output gearset 184 may thus have diameters 140, 142,144, 146, 148, 150 that decrease with each high numbered output gear. Inaccordance with the subject disclosure, the primary first gear diameter124 of the primary first gear 70 is equal to the duplicate first geardiameter 138 of the duplicate first gear 82. It should be appreciatedthat this dimensional relationship between the primary first gear 70 andthe duplicate first gear 82 allows for contemporaneous engagement of theprimary first gear 70 and the duplicate first gear 82.

During operation of the dual-clutch transmission assembly 20 shown inFIG. 8, the at least one transmission input shaft 28, the first shaft162, the second shaft 164, the third shaft 166, the output member 182,and the transmission output shaft 30 all rotate in the same direction.The first gearset 68 and the second gearset 80 receive torque from thethird shaft 166 and the second shaft 164, respectively, in response tocontemporaneous engagement of the first clutch 60 and the second clutch62 during launch of the vehicle. Advantageously, this splits the torquethat is applied to the first and second clutches 60, 62 and reduces heatgeneration in the first clutch 60 and in the second clutch 62.

FIG. 9 illustrates an alternative configuration of the dual-clutchtransmission assembly 20 where there are two transmission input shafts186, 188. The first transmission input shaft 186 is rotatably coupled tothe first input member 158 and the second transmission input shaft 188is rotatably coupled to the second input member 160. The firsttransmission input shaft 186 may be hollow and thus the secondtransmission input shaft 188 may be co-axially arranged within the firsttransmission input shaft 186. It should be appreciated that it thisconfiguration, the first transmission input shaft 186 and the secondtransmission input shaft 188 are capable of rotating in oppositedirections. When the first and second clutches 60, 62 are both engaged,the first shaft 162 rotates with the first transmission input shaft 186and the second shaft 164 rotates with the second transmission inputshaft 188, which may be rotating in a direction that is opposite thefirst shaft 162 and the first transmission input shaft 186.

The first gearset 68, the second gearset 80, the output gearset 184, andthe arrangement of the first and second clutches 60, 62, the first,second, and third shafts 162, 164, 166, and the output member 182 of theconfiguration shown in FIG. 8 are all carried over to the configurationshown in FIG. 9. However, the planetary gearset 168 must be modified toaccommodate the opposite rotating directions of the first transmissioninput shaft 186 and the second transmission input shaft 188.

In this configuration, the ring gear 176 of the planetary gearset 168 isdisposed in meshing engagement with the first set of pinion gears 172and the second set of pinion gears 174 is eliminated. The planetarygearset 168 further includes at least one auxiliary pinion gear 190 thatis rotatably coupled to the first set of pinion gears 172 by carrier180. The planetary gearset 168 also includes an auxiliary sun gear 192that is rotatably coupled to the third shaft 166. By way of example andwithout limitation, the auxiliary sun gear 192 may be fixed to the thirdshaft 166 by a splined, bolted, or welded connection or may be integralwith the third shaft 166. A reverse idler 194 is disposed in meshingengagement with both the auxiliary pinion gear 190 and the auxiliary sungear 192. The reverse idler 194 operates to reverse rotation of theauxiliary sun gear 192 and thus the third shaft 166 relative to thecarrier 180. Accordingly, the second shaft 164, the third shaft 166, andthe output member 182 all rotate in the same direction when the firstshaft 162 and the second shaft 164 are rotating in opposite directions.Because rotation of the third shaft 166 is reversed from rotation of thefirst shaft 162, the first and second gearsets 68, 80 do not bind withthe output gearset 184 when the first and second clutches 60, 62 aresimultaneously engaged. This configuration of the planetary gearset 168thus allows torque to be split between the first and second clutches 60,62 when the dual-clutch transmission assembly 20 includes twotransmission input shafts 186, 188 rotating in opposite directions.

In FIG. 10, an alternative planetary configuration of the dual-clutchtransmission assembly 20 is illustrated. The arrangement of the primaryfirst gear 70 and the duplicate first gear 82 shown yields a planetaryconfiguration of the dual-clutch transmission assembly 20 that is morecompact. Advantageously, the positioning of the duplicate first gear 82in this configuration allows the duplicate first gear 82 to be addedwithout increasing the overall dimensions (i.e. length, height, andwidth) of the dual-clutch transmission assembly 20. As a result,transmission housings from other dual-clutch transmission assembliesthat do not have a duplicate first gear can be utilized with little tono modification.

In FIG. 10, the positions of the primary first gear 70 on the thirdshaft 166, the reverse gear 74 on the third shaft 166, the duplicatefirst gear 82 on the second shaft 164, and the second gear 86 on thesecond shaft 164 have been modified from those shown in FIGS. 8 and 9.With reference to FIG. 10, the primary first gear 70 and the duplicatefirst gear 82 are axially positioned adjacent to one another and areboth disposed in meshing engagement with a common output gear 196 in aside-by-side spaced relationship. The common output gear 196 has acommon output gear diameter 198. The primary first gear 70, the reversegear 74, the third gear 76, and the fifth gear 78 are carried on thethird shaft 166 and rotate with the third shaft 166 if engaged. Thereverse gear 74 is axially positioned at one end of the third shaft 166adjacent to the auxiliary sun gear 192. The primary first gear 70 isaxially positioned at an opposite end of the third shaft 166 that isopposite the auxiliary sun gear 166. The duplicate first gear 82, thesecond gear 86, the forth gear 88, and the sixth gear 90 are carried onthe second shaft 164 and rotate with the second shaft 164 if engaged.The duplicate first gear 82 is axially positioned between the primaryfirst gear 70 (which is on the third shaft 166) and the fourth gear 88(which is on the second shaft 164). The common output gear 196 iscarried on and rotates with the output member 182. The common outputgear 196 is wide enough that it is disposed in meshing engagement withboth the primary first gear 70 and the duplicate first gear 82.Therefore, the primary first gear 70 and the duplicate first gear 82commonly share the common output gear 196 and both the primary firstgear 70 and the duplicate first gear 82 cooperate to drive the commonoutput gear 196 when the first and second clutches 60, 62 are engaged.

During vehicle launch, the primary first gear 70, the duplicate firstgear 82, and the first and second clutches 60, 62 are engaged such thatthe torque applied to the transmission input shaft 28 is split betweenthe first torque flow path 120 and the second torque flow path 122. Thefirst torque flow path 120 passes through the first clutch 60, throughthe planetary gearset 168, through the primary first gear 70, throughthe common output gear 196, and to the output member 182. The secondtorque flow path 122 passes through the second clutch 62, through theduplicate first gear 82, through the common output gear 196, and to theoutput member 182. Accordingly, the first and second torque flow paths120, 122 are re-combined at the common output gear 196. In this way, theduplicate first output gear 108 shown in FIGS. 8 and 9 is eliminated forimproved packaging, reduced cost, and weight savings.

Many modifications and variations of the present invention are possiblein light of the above teachings and may be practiced otherwise than asspecifically described while within the scope of the appended claims.These antecedent recitations should be interpreted to cover anycombination in which the inventive novelty exercises its utility. Itshould be appreciated that any of the various gears may be selectivelyor fixedly coupled to the shaft they are carried on, providing a varietyof different combinations where the various gears can be selectivelyengaged and disengaged as needed to control operation of the dual-clutchtransmission assembly 20 and effectuate shifts. All such variations areconsidered to be within the scope of the subject disclosure. It shouldalso be appreciated that although the dual-clutch transmission assembly20 recited in the claims may be coupled to an engine 22 when thedual-clutch transmission assembly 20 is installed in a vehicle, thepresence or absence of the engine 22 and the vehicle are not intended tobe required under the appended claims.

What is claimed is:
 1. A dual-clutch transmission assembly that splitstorque generated by an engine of a vehicle, the dual-clutch transmissionassembly comprising: a transmission input shaft that receives torquefrom the engine of the vehicle; a transmission output shaft thatsupplies torque to drivetrain components of the vehicle; a firstlayshaft; a first input hub that is disposed adjacent said firstlayshaft and that is rotatably coupled with said transmission inputshaft; a second layshaft spaced from said first layshaft; a second inputhub that is disposed adjacent said second layshaft and that is rotatablycoupled with said transmission input shaft; a first clutch disposedbetween and interconnecting said first input hub and said firstlayshaft, said first clutch selectively coupling rotation of said firstinput hub with said first layshaft; a second clutch disposed between andinterconnecting said second input hub and said second layshaft, saidsecond clutch selectively coupling rotation of said second input hubwith said second layshaft; a first gearset rotatably coupled to andcarried on said first layshaft that transfers torque between said firstlayshaft and said transmission output shaft; a second gearset rotatablycoupled to and carried on said second layshaft that transfers torquebetween said second layshaft and said transmission output shaft; saidfirst gearset including a primary first gear having a primary first geardiameter; said second gearset including a duplicate first gear having aduplicate first gear diameter that is equal to said primary first geardiameter; and each of said first and second layshafts receiving torquefrom said transmission input shaft in response to contemporaneousengagement of said primary first gear, said duplicate first gear, saidfirst clutch, and said second clutch to split the torque applied to saidfirst and second clutches, wherein said first gearset further includes aplurality of odd numbered gears and said second gearset further includesa plurality of even numbered gears.
 2. The dual-clutch transmissionassembly as set forth in claim 1 wherein said primary first gear isdisposed along said first layshaft between said first clutch and saidplurality of odd numbered gears.
 3. The dual-clutch transmissionassembly as set forth in claim 2 wherein said duplicate first gear isdisposed along said second layshaft adjacent said plurality of evennumbered gears such that said plurality of even numbered gears aredisposed between said second clutch and said duplicate first gear. 4.The dual-clutch transmission assembly as set forth in claim 1 whereinsaid plurality of odd numbered gears of said first gearset have geardiameters that increase with each higher numbered gear and saidplurality of even numbered gears of said second gearset have geardiameters that increase with each higher numbered gear.
 5. Thedual-clutch transmission assembly as set forth in claim 1 furthercomprising: a transmission input gear rotatably coupled to and carriedon said transmission input shaft.
 6. The dual-clutch transmissionassembly as set forth in claim 5 further comprising: a first layshaftinput gear rotatably coupled to and carried on said first input hub thatis arranged in meshing engagement with said transmission input gear; anda second layshaft input gear rotatably coupled to and carried on saidsecond input hub that is arranged in meshing engagement with saidtransmission input gear opposite said first layshaft input gear.
 7. Thedual-clutch transmission assembly as set forth in claim 1 wherein saidfirst and second layshafts are parallel to one another and aretransversely spaced.
 8. The dual-clutch transmission assembly as setforth in claim 1 further comprising: a single intermediate shaftextending parallel to and transversely spaced from said first and secondlayshafts.
 9. The dual-clutch transmission assembly as set forth inclaim 8 wherein said single intermediate shaft is positioned betweensaid first layshaft and said second layshaft.
 10. The dual-clutchtransmission assembly as set forth in claim 8 further comprising: athird gearset rotatably coupled to and carried on said singleintermediate shaft that is arranged in meshing engagement with saidfirst gearset; and a fourth gearset rotatably coupled to and carried onsaid single intermediate shaft that is arranged in meshing engagementwith said second gearset.
 11. The dual-clutch transmission assembly asset forth in claim 10 wherein said third gearset and said fourth gearsethave gears that are grouped together on said single intermediate shaftsuch that said gears of said third gearset are disposed on one side ofsaid single intermediate shaft and said gears of said fourth gearset aredisposed on an opposite side of said single intermediate shaft.
 12. Thedual-clutch transmission assembly as set forth in claim 10 wherein saidthird gearset and said fourth gearset have gears that are sequentiallyarranged on said single intermediate shaft such that said gears of saidthird gearset alternate with said gears of said fourth gearset alongsaid single intermediate shaft.
 13. The dual-clutch transmissionassembly as set forth in claim 8 further comprising: a first output gearrotatably coupled to and carried on said single intermediate shaft,wherein said first output gear, said primary first gear, and saidduplicate first gear are aligned with one another, and wherein saidprimary first gear and said duplicate first gear are arranged in meshingengagement with said first output gear such that both said primary firstgear and said duplicate first gear cooperate to drive said first outputgear when said first and second clutches are engaged.
 14. Thedual-clutch transmission assembly as set forth in claim 13 furthercomprising: a reverse gear rotatably coupled to and carried on saidfirst layshaft; a second gear rotatably coupled to and carried on saidsecond layshaft; a second output gear rotatably coupled to and carriedon said single intermediate shaft; and a reverse idler gear disposedbetween said reverse gear and said second output gear in meshingengagement, wherein said reverse gear, said second gear, said secondoutput gear, and said reverse idler gear are aligned with one another,and wherein said second gear and said reverse idler gear are arranged inmeshing engagement with said second output gear such that said secondoutput gear is driven in one rotational direction by said second gearwhen said first clutch is disengaged and said second clutch is engagedand such that said second output gear is driven in an oppositerotational direction by said reverse idler gear when said first clutchis engaged and said second clutch is disengaged.
 15. The dual-clutchtransmission assembly as set forth in claim 8 further comprising: aprimary first output gear that is rotatably coupled to and carried onsaid single intermediate shaft and that is arranged in meshingengagement with said primary first gear; a duplicate first output gearthat is rotatably coupled to and carried on said single intermediateshaft and that is arranged in meshing engagement with said duplicatefirst gear; a second gear rotatably coupled to and carried on saidsecond layshaft; a third gear rotatably coupled to and carried on saidfirst layshaft; a second output gear that is rotatably coupled to andcarried on said single intermediate shaft and that is arranged inmeshing engagement with said second gear; and a third output gear thatis rotatably coupled to and carried on said single intermediate shaftand that is arranged in meshing engagement with said third gear.
 16. Thedual-clutch transmission assembly as set forth in claim 15 furthercomprising: a fourth gear rotatably coupled to and carried on saidsecond layshaft; a fourth output gear that is rotatably coupled to andcarried on said single intermediate shaft and that is arranged inmeshing engagement with said fourth gear; and a transfer clutchextending longitudinally between said third and fourth output gears,wherein engagement of said transfer clutch rotatably couples said thirdoutput gear with said fourth output gear.
 17. The dual-clutchtransmission assembly as set forth in claim 15 further comprising: afirst transfer gear that is rotatably coupled to and carried on saidfirst layshaft and that is arranged in meshing engagement with saidsecond output gear; and a second transfer gear that is rotatably coupledto and carried on said second layshaft and that is arranged in meshingengagement with said third output gear, wherein selective engagement ofsaid first and second transfer gears with said first and secondlayshafts respectively provides multiple ratios when said second geardrives said second output gear and multiple ratios when said third geardrives said third output gear.
 18. The dual-clutch transmission assemblyas set forth in claim 1 further comprising: a first intermediate shaftextending parallel to and transversely spaced from said first layshaft,said first intermediate shaft disposed adjacent said first layshaft andpositioned between said first layshaft and said second layshaft; and asecond intermediate shaft extending parallel to and transversely spacedfrom said second layshaft, said second intermediate shaft disposedadjacent said second layshaft and positioned between said first layshaftand said second layshaft.
 19. The dual-clutch transmission assembly asset forth in claim 18 further comprising: a third gearset rotatablycoupled to and carried on said first intermediate shaft that is arrangedin meshing engagement with said first gearset; and a fourth gearsetrotatably coupled to and carried on said second intermediate shaft thatis arranged in meshing engagement with said second gearset.
 20. Thedual-clutch transmission assembly as set forth in claim 19 furthercomprising: a transmission output gear rotatably coupled to and carriedon said transmission output shaft; a first intermediate shaft outputgear rotatably coupled to and carried on said first intermediate shaftthat is arranged in meshing engagement with said transmission outputgear; and a second intermediate shaft output gear rotatably coupled toand carried on said second intermediate shaft that is arranged inmeshing engagement with said transmission output gear opposite saidfirst intermediate shaft output gear.
 21. The dual-clutch transmissionassembly as set forth in claim 1 wherein said plurality of odd numberedgears of said first gearset and said plurality of even numbered gears ofsaid second gearset provide different forward gear ratios.
 22. Thedual-clutch transmission assembly as set forth in claim 21 wherein saidplurality of odd numbered gears of said first gearset and said pluralityof even numbered gears of said second gearset have different diameters.23. A dual-clutch transmission assembly comprising: a transmission inputshaft; a transmission output shaft; a first layshaft; a first input hubaligned with said first layshaft that is disposed adjacent saidtransmission input shaft and that is rotatably coupled with saidtransmission input shaft; a second layshaft spaced from said firstlayshaft; a second input hub aligned with said second layshaft that isdisposed adjacent said transmission input shaft and that is rotatablycoupled with said transmission input shaft; a first clutch disposedbetween and interconnecting said first input hub and said firstlayshaft, said first clutch selectively coupling rotation of said firstinput hub with rotation of said first layshaft; a second clutch disposedbetween and interconnecting said second input hub and said secondlayshaft, said second clutch selectively coupling rotation of saidsecond input hub with rotation of said second layshaft; a first gearsetrotatably coupled to and carried on said first layshaft; a secondgearset rotatably coupled to and carried on said second layshaft; afirst intermediate shaft adjacent said first layshaft; a secondintermediate shaft adjacent said second layshaft; a third gearsetrotatably coupled to and carried on said first intermediate shaft thatis arranged in meshing engagement with said first gearset; a fourthgearset rotatably coupled to and carried on said second intermediateshaft that is arranged in meshing engagement with said second gearset;said first gearset including a primary first gear having a primary firstgear diameter; said second gearset including a duplicate first gearhaving a duplicate first gear diameter that is equal to said primaryfirst gear diameter; and each of said first and second layshaftsreceiving torque from said transmission input shaft in response tocontemporaneous engagement of said primary first gear, said duplicatefirst gear, said first clutch, and said second clutch to evenly splitthe torque applied to said first and second clutches and reduce heatgeneration in said first clutch and in said second clutch.
 24. Thedual-clutch transmission assembly as set forth in claim 23 wherein saidfirst gearset further includes a plurality of odd numbered gears andsaid second gearset further includes a plurality of even numbered gears.25. The dual-clutch transmission assembly as set forth in claim 23wherein said first gearset further includes a first plurality of gearsand said second gearset further includes a second plurality of gears.26. The dual-clutch transmission assembly as set forth in claim 25wherein said first plurality of gears of said first gearset and saidsecond plurality of gears of said second gearset provide differentforward gear ratios.
 27. The dual-clutch transmission assembly as setforth in claim 25 wherein said first plurality of gears of said firstgearset and said second plurality of gears of said second gearset havedifferent diameters.
 28. The dual-clutch transmission assembly as setforth in claim 27 wherein said third gearset includes a third pluralityof gears and said fourth gearset includes a fourth plurality of gears.29. The dual-clutch transmission assembly as set forth in claim 28wherein said third plurality of gears of said third gearset and saidfourth plurality of gears of said fourth gearset have differentdiameters.
 30. The dual-clutch transmission assembly as set forth inclaim 29 wherein said first plurality of gears of said first gearsethave diameters that increase with each higher numbered gear, and saidsecond plurality of gears of said second gearset have diameters thatincrease with each higher numbered gear.
 31. The dual-clutchtransmission assembly as set forth in claim 30 wherein said thirdplurality of gears of said third gearset have diameters that decreasewith each higher numbered gear, and said fourth plurality of gears ofsaid fourth gearset have diameters that decrease with each highernumbered gear.